To show a preview of a form image, use the :hint form parameter, like so (thank to Greg Tangey for this on the [mailing list](http://groups.google.com/group/activeadmin/browse_thread/thread/ed00f503d8316035/09f7c9f895f619b6?lnk=gst&q=form+image#09f7c9f895f619b6):

```ruby
f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => image_tag(f.object.cover_page.url) 
  f.input :cover_page_cache, :as => :hidden 
end
```

Of course you can still do all the processing you are used to from PaperClip or CarrierWave:

```ruby
f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => image_tag(f.object.cover_page.url(:thumb)) 
  f.input :cover_page_cache, :as => :hidden 
end
```

Also you can prevent error if image not uploaded yet:

```ruby
f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => f.object.cover_page.present? \
    ? image_tag(f.object.cover_page.url(:thumb))
    : content_tag(:span, "no cover page yet")
  f.input :cover_page_cache, :as => :hidden 
end
```
Remember the `:image_cache` input to get previews in non-saved records with e.g. CarrierWave. See Ryan's [Railscast on CarrierWave](http://railscasts.com/episodes/253-carrierwave-file-uploads) for more information.